1. Field of the Invention
The present invention relates to an improvement in inertial impact sensors having particular utility in automotive vehicle inflatable air bag restraint systems. The sensor senses an impact and actuates a gas generator to inflate an air bag for restraining forward movement of seated occupants during the critical instant of collision impact.
2. Description of the Prior Art
Realizing that automotive vehicle crash restraint systems requiring positive effort on the part of the user for effectiveness have largely been ignored by the population intended to be protected, governmental safety programs have tended to emphasize automatic restraint systems, such as gas or air bags.
A gas filled bag has been demonstrated to be an effective device for protecting automotive occupants during crashes. The details of crash bag systems have been widely discussed, as have the reasons for selection of pyrotechnic devices when dependable gas supplies for the rapid deployment of crash bags are required. The operational constraints of crash bags are also well known. The system must supply non-toxic gas to inflate the bag because the bag generally is vented into the interior of the vehicle on deflation and because of the possibility of rupture in an actual crash situation. The gas must inflate the bag at a temperature which the vehicle occupants to be protected can tolerate. The time period for attainment of maximum inflation has been determined to be from 20 to 100 milliseconds after actuation by an impact sensor.
An impact sensor senses an impact and actuates a gas generator to inflate a crash bag located between the vehicle front seat occupants and the windshield-dashboard area. As noted above, the time to accomplish this operation is very short. Assuming a head-on collision of an automobile travelling 60 miles per hour (88 feet per second) with a stationary barrier, an inelastic impact would result in the occupants moving forward twelve inches in approximately the first 10 milliseconds after initial contact. Since some elasticity is present in the crushing of metallic structure, the time between the first structural contact and the movement of the vehicle occupants is of the order of 30 milliseconds. The system must function and the bag must be deployed in this time period in order to be effective.
Impact sensors located directly behind the front bumper of the vehicle are in a region which will experience the first effects of a crash and thus allow a maximum time for operation. Several impact sensors may be strategically placed in this area to accommodate the various impact modes that are possible.
The apparatus components comprising the system must be safe to handle and store prior to installation. Such components also must be adaptable to mass production, lend themselves to easy installation, and not introduce an unreasonable hazard at the time of installation or during the life of the vehicle. Additionally, the system must assure reliable operation during the life of the vehicle, which may be 10 years or more.
Sensors which utilize inertial forces to cause a firing pin to impact an explosive primer are known in the prior art. Thus, in U.S. Pat. No. 2,324,243, granted on July 13, 1943 to L. S. Serog, there is disclosed a sensor for causing the detonation of a projectile upon impact. The Serog sensor involves the compression of a spring using the inertial forces of impact, and then release of the spring and the firing pin by means of a latching arrangement.
U.S. Pat. No. 2,857,842 granted on Oct. 28, 1958 to K. O. Malm discloses a sensing device for a land mine comprising an overcenter belleville spring which, when mechanically triggered, activates a firing pin to initiate an explosive primer.
U.S. Pat. No. 3,552,769, granted to R. M. Kemmerer et al on Jan. 5, 1971, discloses a sensor that is mounted behind the front bumper of a vehicle and which utilizes the inertial forces of impact to actuate a gas generator to effect the deployment of a crash bag. The Kemmerer et al arrangement consists of compressing a spring using the inertial forces of impact and then releasing the spring and a firing pin with a ball-detent latch.
In U.S. Pat. No. 4,167,276, granted on Sept. 11, 1979 to L. E. Bell et al, an impact sensing device for actuating the inflating unit of a vehicle air bag restraint system is mounted adjacent the inflating unit on the steering wheel of the vehicle. The impact sensing device includes an inertial mass, a ball, that is pulled off a magnet by the impact force. The inertial mass then strikes a lever which releases a firing pin which has been preloaded with a spring to impact an explosive primer.
Each of the above prior art sensors for activating a firing pin to initiate an explosive primer is characterized in that the only source of energy propelling the firing pin to impact the explosive primer is the associated spring. That is to say, in each of the Serog, Kemmerer et al and Bell et al patents the inertial forces of an inertial mass are utilized only to trigger the release of the firing pin for actuation by a spring. No inertial forces are involved in the Malm patent, the triggering for the release of the spring being mechanical as when treaded upon or actuated by a car or the like rolling over the land mine.
An impact sensing device that utilizes both a spring and the inertial force of a decelerating mass to generate the energy to initiate an explosive primer is disclosed in my U.S. Pat. No. 4,552,380 granted on Nov. 12, 1985 and assigned to Morton Thiokol, Inc., the assignee of the present invention and application. The impact sensing device there disclosed includes an over-center spring arrangement that allows the energy of the inertial force in addition to that of the spring arrangement to be applied to a firing pin for impacting an explosive primer. As in the aforementioned Bell et al patent, however, the impact sensing device is mounted adjacent the inflating unit on the steering wheel of the vehicle.
While mounting the impact sensing device adjacent the inflating unit on the steering wheel of the vehicle allows the vehicle restraint system to be self-contained, the impact sensing device, as above mentioned, is not then in a region which will experience the first effects of a crash. As a result, there is a delay in the reaction to the crash and a corresponding reduction in the amount of time allowed for operation of the rest of the system.
There is thus a need and a demand for further improvement in impact sensor arrangements for automotive crash bag systems. The present invention was devised to fill this technological gap.